Process of removing scale from titanium



PROCESS OF REMOVING SCALE FROM TITANIUM Carl D. Macl herson, Detroit, Mich., assignor to Wayne Foundry & Stamping Co., Detroit, Mich.

No Drawing. Application January 14, 1955, Serial No. 481,963

3 Claims. (Cl. 134-3) workpiece in a heated state of from 800-1200 F.

At such an elevated temperature, corrosion products form on the surface which are very dense and adherent and consequently difiicult to remove. In addition, metal from the die parts frequently adheres to thepiece, es pecially if zinc base alloy dies are used for drawing or stamping.

Various types of cleaning processes have been used for removing the scale and the die-metal contamination, but so far these have been objectionable from the standpoint of cost and danger to the workmen. The salt bath solutions now in use require large expenditures for capital equipment and the cost of operating the baths is very high. Furthermore, the use of salt bath solutions causes deleterious effects to the parts being cleaned because of the formation of an electrical potential between the parts and the suspension racks.

It is the prime object of my invention to provide a method of descaling titanium in a safe, economical manner.

A further object is to provide a method of cleaning formed titanium parts of contamination picked up during fabrication.

Other objects and advantages of my invention will be apparent from the following description.

My improved method comprises the following steps:

1. The piece is placed in a soakingtank containing a commercially obtainable alkali cleaner in solution, the temperature of the bath being preferably maintained at 180 F. to 200 F. This bath is intended to remove dirt, oil and the like picked up during fabrication. Immersion for a period of one minute has been found to be adequate in most instances.

2. The piece is thoroughly rinsed in a cold water rinse.

United States Patent perature.

3. The piece is immersed for approximately one minute in an 18%-20% commercial hydrochloric acid solution at room temperature. This bath removes the zinc alloy which may have adhered to the piece during the stamping or drawing operation.

4. Cold water rinse.

5. The piece is dried, preferably by an air blast so that the part remains at room temperature.

6. Immersion for approximately one minute or less, depending on the temperature at which the scale was formed, in a bath of hydrofluoric acid (commercial grade) at room temperature. This particular concentration has been found effective in removing the scale formed on the surface of the metal during heat treating without appreciably attacking or having an injurious effect on the base metal itself.

7. Cold water rinse.

8. Second cold water rinse (optional).

9. Immersion for approximately one minute in a solution containing 3% hydrofluoric acid and 20% nitric acid at room temperature. This bath brightens and passivates the surface of the titanium.

10. Final cold water rinse.

It will be noted that all of the above mentioned operations except alkali cleaning are carried on at room tem- Indeed, the entire process can be carried on by use of ordinary dip tanks and other equipment commonly used in metal working plants.

I have found that fabricated titanium parts that have picked up contamination from dies and scale from heat treating can be easily restored to clean condition and original surface finish without damage by use of the above described cleaning procedure.

I claim:

1. In a process of removing scale from titanium, the step of immersing the metal in a hydrofluoric acid solution of approximately 60% concentration at room temperature.

2. The process of cleaning and descaling titanium after fabrication at high temperature which comprises the following steps:

1. Soak in hot alkali bath;

2. Cold water rinse;

3. Immersion in hydrochloric acid bath of approximately 20% concentration at room temperature;

4. Cold water rinse;

5. Dry;

6. Immersion in hydrofluoric acid bath of approximately 60% concentration at room temperature;

7. Cold water rinse.

3. The process of claim 2, including the additional step of immersing the metal in a bath containing 3% hydrofluoric acid and 20% nitric acid at room temperature.

No references cited. 

1. IN A PROCESS OF REMOVING SCALE FROM TITANIUM, THE STEP OF IMMERSING THE METAL IN A HYDROFLUORIC ACID SOLUTION OF APPROXIMATELY 60% CONCENTRATION AT ROOM TEMPERATURE. 